From magazines and novels to review of important document, reading forms a critical part of our lives, and many reading tasks involve a rich interaction with the text. This rich interaction, known as active reading, can be conducted to answer questions, perform analysis, or obtain information. Active reading can involve highlighting, annotating, outlining, note-taking, comparing, and searching. As a result, active reading generally demands more of a reading medium than simply an ability to advance pages.
Although paper supports bimanual interaction and freeform annotation within the boundaries of a single page, paper lacks the flexibility to provide, for example, content rearrangement, document overviews, and annotation outside of page boundaries. Additionally, although the tangibility of paper supports some rapid forms of navigation, such as dog-earing and bookmarking with a finger, paper provides little flexibility to create a customized navigational structure. Modern pen-based computerized tablets do a fine job of imitating paper, which benefits users by providing a familiar medium, but as a result, these pen-based tablets suffer from the same limitations as paper. Thus, neither paper nor modern computer systems adequately facilitate active reading.